Spectral emissivity measurement facility for solar absorbing coating based on integrating-sphere reflectometry


Y. Zhang1 and J. Dai1

1Harbin Institute of Technology, P.R. China

Keywords: spectral emissivity; integrating-sphere
property: measurement facility
material: solar absorbing coating

The spectral emissivity of solar absorbing coating is significant to investigate the performance that the coating contributes to absorb more energy of solar radiation through its high emissivity in range of solar spectrum, and at the mean time radiate less energy through its low emissivity in other spectral range at operating temperatures[1].

A new facility covers the spectral range of 0.4μm to 10μm and temperatures from 300K to 1000K for the measurement of spectral emissivity of solar absorbing coating that employs a set of integrating-sphere spectrum reflectometry has been built[2], which consist of several devices and measurement components: a white board polished and plated with Al[3]; a radiation source modulated by a adjustable-speed chopper; three grating monochromators with motion control system; a integrating-sphere made up of a glass and vacuum-plated with Al in the internal surface of sphere ; a sample hardware for heating and system of accurate temperature control and measurement[4]; Hg:Cd:Te(MCT) detector and electronic instruments. The facility is operated by the following procedure: the modulated radiation emitted from radiation source is converted to monochromatic radiation through the monochromator moved to the position between radiation source and integrating-sphere according to its wavelength coverage. After passing through the entrance port of integrating sphere the monochromatic radiation is projected onto the surface of sample or whiteboard mounted on the hardware at 8 degree from the direction of the incident radiation. At last the reflected radiations confined in the integrating sphere are detected by MCT located at the top. In the same manner,the different wavelength radiations reflected from sample and white board are detected automatically under the control of computer software written using Labview, spectral emissivity is obtained by a simple calculation.

The spectral emissivity of several coatings measured by this facility is agreed with that measured by methods of radiant energy comparison using Fourier Transform Infrared Spectrometer (FTIR) and consistent with the literature[5]. The benefit of this facility is the trouble that spectral emissivity is difficult to be measured at room temperature is solved as well as the operation of measurement is automatic.

References
  1. C.J.Winter. Sol Energy Mater. Sol. Cells. 24(1991)

  2. L.M. Hanssen. Appl. Opt. 40(2001)

  3. J. M. Dai, Y. Fan, Z. X. Chu. Int. J. Thermophys. 23,5(2000)

  4. P. Coppa, J. M. Dai, G. Ruffino. Int. J. Thermophys. 14,3 (1993)

  5. Z. W. Wang, J. M. Dai, X. W. He. J. Infrared Millim. Waves. 29, 5(2010)

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